Community is Community
The last point is certainly true - there are some thing you can get from a good real-life friendship that you can't get over the Internet. But that doesn't make Internet relationships valueless.
I posted awhile back about my younger's brother's unhappy experience with a gym teacher. When he came home that day, he was the first one home, and was extremely upset. He logged onto World of Warcraft, on a draenei paladin character.
One of the multiplayer elements in World of Warcraft is guilds. Guilds are communities of players who work together. They have a shared bank and various perks based on how experienced the guild is. Many guilds have regularly scheduled events such as raids (where 10 or 20 high-level players take on a very difficult dungeon together). And, most importantly, they have a guild chat. You can tell which other guild members are online, and you can talk to them.
That's what my brother did. His draenei paladin, his worgen druid, and my night elf hunter are all part of the same guild. On that day, he talked to two guild members, the guild leader and a member who is apparently a soon-to-be mother. He told them what had happened and how he felt, and they comforted him. By the time Mom got home, he was calmed down.
There's another person I know of who's been helped more dramatically. He hangs out on the TVTropes 'On Topic Conversations' forum, under the username DJay32. In November of last year, he posted a thread titled "Could someone.. help? A bit? Please? *Massive Story Inside*". In that first post, he told us that he was 15 years old and being physically attacked by his father and older brother, and not getting enough food.
The thread is now 60+ pages long, with more than a thousand posts. The other members of this forum told him that he was being abused, that he did not deserve such treatment and should contact social services. Sadly, social services didn't hold up their part, delaying until his sixteenth birthday and then claiming they "don't foster sixteen year olds". But the members of this forum have stuck with him, advising him on various routes to seek help, the locations of nearby food banks, and how to get around his parents' efforts to keep him from telling on them. And they've supported him emotionally.
I wouldn't be surprised if TVTropes forum is keeping this kid alive. He has been losing time, waking up to find that he's written and drawn things depicting suicidal thoughts. He says he wants to die, but can't kill himself because of his friends telling him suicide is a bad idea. And when his Internet connection goes down, he gets desperate. He doesn't really have any support other than the Internet, since his family recently moved and he's very shy in person.
Internet relationships, to be clear, are real. They involve real people interacting with other real people, and can have real effects on people. They are different from in-person relationships, but that doesn't make them worthless.